Portable working machines are known which comprise a motive power source carried on a case for producing a rotational motion, a reduction mechanism for reducing speed of the rotational motion from the motive power source, and a motion conversion mechanism for converting the rotational motion with reduced speed into a linear reciprocating motion of a cutting blade. The reduction mechanism and the motion conversion mechanism are mounted within the case, and the cutting blade projects from the case. One example of such a known portable working machine is disclosed in Japanese Patent Laid-Open Publication (JP-A) No. 09-271233.
As shown in FIG. 12 hereof, the disclosed portable working machine 200 includes a machine body 201, a motive power source 202 for producing a rotational motion, a reduction mechanism 203 connected via a centrifugal clutch (not shown) to the motive power source 202 for reducing speed of the rotational motion from the motive power source 202, and a motion conversion mechanism 204 connected to the reduction mechanism 203 for converting the rotational motion of reduced speed into linear reciprocating motion of a movable cutting blade 205 that is sidably movable relative to a stationary cutting blade 206 secured to a case 207.
The portable working machine 200 may be dropped onto the ground or roughly handled by the operator during use or transportation. In such instance, the case 207 may be damaged or broken due to an impact applied thereto. This may also cause a problem that a coupling structure provided between the motive power source and the reduction mechanism is also damaged or broken due to the effect of the impact force because the coupling structure including a clutch is susceptible to damage.
A further drawback associated with the known portable working machine 200 resides in that due to the presence of protrusions including heads of screw fasteners on a lower surface of the case 27, smooth sliding movement of the portable working machine on a cut or trimmed hedge surface cannot be achieved during a hedge trimming operation, resulting in a limited working efficiency of the portable working machine.